[5] Despite only being signed to a schoolboy contract,[4] Onariase received his maiden call into the first team squad for a Premier League match versus Arsenal on 14 March 2015 and remained an unused substitute during the 3–0 defeat.

[7] On 29 January 2016, Onariase signed an 18-month contract with the Development Squad at Championship club Brentford for an undisclosed fee.

[6] Onariase was an unused substitute on two further occasions and on 1 January 2017,[6] he joined League Two strugglers Cheltenham Town on loan until the end of the 2016–17 season.

[10] After signing a new two-year contract on 22 June 2017,[8] Onariase was included in the first team squad for its 2017–18 pre-season training camp in France.

[12] On 31 August 2017, Onariase joined League One club Rotherham United on a two-year contract for an undisclosed fee.

[19] On 25 October 2018, Onariase joined National League club Dagenham & Redbridge on a loan which was later extended until the end of the 2018–19 season.

[6][22] On 3 August 2020, Onariase signed a two-year contract with League Two club Scunthorpe United for an undisclosed fee.

[28] On 15 March 2022, Onariase returned to National League club Dagenham & Redbridge for an undisclosed fee and signed a contract running until the end of the 2023–24 season.